Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 230003
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
603 PM CST MON DEC 22 2014

UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE
AND NEW INFORMATION ADDED TO UPDATE SECTION

.UPDATE...
ISSUED AT 551 PM CST MON DEC 22 2014

LEAD BAND OF PCPN SURGING NWD ACRS THE SRN PART OF THE FCST AREA
EARLY THIS EVENING. PCPN GENERALLY LIQUID OR A MIX AT THE
ONSET...THEN CHANGING TO MAINLY SNOW AS EVAP COOLING DOWN TO THE
WET-BULB TEMP KNOCKS LOW-LEVEL TEMPS BACK A COUPLE DEGREES. WAA IN
THE 925-850 MB LAYER SHOULD EVENTUALLY LEAD TO A CHANGE BACK TO
LIQUID OVER E-C WI LATER TNGT...THOUGH TIMING OF THAT IS HARD TO
PIN DOWN. WITH GROUND TEMPS GENERALLY AOA FREEZING...ITS HARD TO
SEE GETTING MORE THAN A SLUSHY ACCUMULATION ON GRASSY AREAS THIS
EVENING.

SLIGHTLY COLDER TEMPS BACK TO THE NW IN C-NE WL ALLOW FOR MORE
ACCUMULATION IN THOSE AREAS...AND SOME TRAVEL PROBLEMS WL LIKELY
DEVELOP THERE AS THE EVENING PROGRESSES.

DESPITE NOW BEING WITHIN 48 HRS OF THE POSSIBLE EVENT...THERE IS
STILL A HIGH DEGREE OF UNCERTAINTY ON THE POSSIBILITY OF HAVING
SECONDARY CYCLONE RUNNING UP THE FRONT IMPACT THE AREA ON XMAS
EVE.

.SHORT TERM...TONIGHT AND TUESDAY
ISSUED AT 249 PM CST MON DEC 22 2014

PLENTY OF POTENTIAL PITFALLS IN THIS FCST OVER THE NEXT 24 HOURS
AS A LARGE DYNAMIC SYSTEM GRADUALLY MOVES INTO THE REGION. THE
MAIN FCST DILEMA TO BE PCPN TYPE OVER MOST OF THE FCST AREA AS
WARMER AIR AT THE SFC TRIES TO LIFT NORTH AND WL BE COUNTERED BY
DYNAMIC COOLING TRYING TO KEEP THE ATMOSPHERIC COLUMN COOLER.

THE 20Z MSAS SFC ANALYSIS INDICATED A PAIR OF LOW PRES SYSTEMS
OVER THE NRN AND CNTRL PLAINS. A WRMFNT EXTENDED FROM THE CNTRL
PLAINS EWD INTO THE OHIO RIVER VALLEY. THE RADAR MOSAIC SHOWED A
LARGE BAND OF PCPN LIFTING NORTH FROM THE MIDWEST INTO THE GREAT
LAKES/UPR MS VALLEY. THIS PCPN WAS MAINLY IN THE FORM OF RAIN...
ALTHO SOME LIGHT SNOW OR SLEET WERE MIXING IN AT TIMES.

A CLOSED UPR LOW...LOCATED WITHIN THE BROAD CNTRL CONUS LONGWAVE
TROF...IS FCST TO MOVE FROM THE CNTRL PLAINS TO THE MIDWEST TNGT.
AS THIS TAKES PLACE...THE PAIR OF SFC LOWS WL CONSOLIDATE AND LIFT
NEWD INTO NE IA BY DAYBREAK WITH THE WRMFNT PULLING NORTH TO NEAR
THE WI/IL BORDER. THE LARGE SLUG OF GULF MOISTURE...OVERRUNNING
THE WRMFNT AND AHEAD OF A NRN MOVING SHORTWAVE...WL CONT TO
OVERSPREAD THE REST OF WI THIS EVENING WITH PCPN CONTINUING THRU
THE NGT. PCPN TYPE TO BE THE BIGGEST FCST ISSUE AS SFC TEMPS ARE
FCST TO BE AROUND FREEZING N-CNTRL WI TO THE MID 30S E-CNTRL WI
AND THE 8H 0C ISOTHERM TO BE LIFTING NW OVRNGT. CURRENT THINKING
IS FOR AN INCH OR TWO OF SNOW TO FALL NW OF A LINE FROM ISW-MNM
WITH LESSER AMOUNTS ACROSS E-CNTRL WI WHERE MORE RAIN IS
ANTICIPATED.

PCPN WL PICK UP IN INTENSITY LATE TNGT THRU TUE MORNING AS THIS
DYNAMIC SYSTEM HEADS INTO THE WRN GREAT LAKES REGION. PCPN TYPE WL
CONT TO BE A MAJOR FCST HEADACHE...ESPECIALLY OVER THE SE HALF OF
NE WI WHERE THE STRONG DYNAMICS MAY PROVIDE ENUF COOLING TO ALLOW
THE MIXED PCPN OR ALL RAIN TO BRIEFLY CHANGE TO ALL SNOW...DESPITE
SFC TEMPS IN THE UPR 30S. THIS COULD PROVIDE FOR A QUICK INCH OR
TWO OF SNOW FROM ROUGHLY STE-GRB-IMT BACK TO STE DURING THE
MORNING. THIS AREA IS ALSO TO RESIDE ON THE NOSE OF AN INCOMING
DRY SLOT WHERE LIFT WL BE MAXIMIZED. FOR N-CNTRL WI WHERE THE PCPN
TO REMAIN ALL SNOW...LOOK FOR AN ADDITIONAL 2 TO 4 INCHES OF
ACCUMULATION TO OCCUR.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY
ISSUED AT 249 PM CST MON DEC 22 2014

SLOW MOVING SYSTEM WILL CONTINUE TO DRIFT OVER THE GREAT LAKES
REGION TUESDAY NIGHT INTO WEDNESDAY NIGHT. LIGHT WRAP AROUND PCPN
WILL GRADUALLY DEPART THE NORTHWEST HALF OF THE STATE TUESDAY
EVENING WHILE A DRY SLOT DRIVES NORTHEASTWARD INTO MUCH OF EASTERN
WISCONSIN.

OF NOTICE FOR WEDNESDAY INTO WEDNESDAY NIGHT IS THE SUBTLE SHIFT
WESTWARD WITH THE NEW PCPN SHIELD DUE TO PHASING OF THE GREAT
LAKES SYSTEM WITH SOUTHERN STREAM ENERGY. WILL CONFINE HIGHER POPS
ALONG THE LAKESHORE AND LATER RUNS CAN CONTINUE TO UP POPS AND
INCREASE COVERAGE IF THIS TREND CONTINUES. OTHERWISE QUIET
WEATHER FOR XMAS DAY AT THIS TIME.

PROGS ARE IN GOOD AGREEMENT WITH A SURFACE LOW WITH MID LEVEL
TROUGH SLIDING OVER THE AREA TOWARD FRIDAY NIGHT. TEMPERATURES MAY
BE WARM ENOUGH FOR A RAIN SNOW MIX OVER EAST CENTRAL WISCONSIN
BUT WILL KEEP IT SNOW DUE TO OVERNIGHT TIMING. ANOTHER POSSIBLE
FRONTAL SYSTEM MAY SLIDE OVER THE AREA EARLY NEXT WEEK. THIS
EARLY NEXT WEEK SYSTEM MAY BE FOLLOWED WITH SOME COLDER AIR MASS
BUT THE DURATION LOOKS MINIMAL ON THE RECENT MODEL RUNS.
&&

.AVIATION...FOR 00Z TAF ISSUANCE
ISSUED AT 551 PM CST MON DEC 22 2014

IFR OR POORER FLIGHT CONDITIONS EXPECTED THE NEXT 24 HRS. PCPN WL
OVERSPREAD THE AREA FM THE S THIS EVENING. MID-LVL DRY SLOT
DRIVING INTO THE AREA FM THE S WL LIKELY SHUT PCPN DOWN TO DZ/FZDZ
OVER AT LEAST THE SE 1/2 OF THE AREA TOMORROW...BUT CIGS AND VSBYS
WL REMAIN LOW DUE TO PLENTIFUL LOW-LEVEL MOISTURE.
&&

.HYDROLOGY...
ISSUED AT 249 PM CST MON DEC 22 2014

MILD CONDITIONS ARE EXPECTED OVER EAST CENTRAL WISCONSIN THROUGH
WEDNESDAY ALONG WITH THE POTENTIAL OF UP TO 0.25 TO 0.40 INCHES OF
RAIN TONIGHT INTO TUESDAY. WHILE THE RAIN WILL PRODUCE SOME
RUNOFF...PRIMARY ISSUE IS THE AFFECTS ON ICE CONDITIONS ON AREA
RIVERS AND LAKES.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM CST
TUESDAY FOR WIZ005-010>013-018>021-030-031.
&&

$$

UPDATE.........SKOWRONSKI
SHORT TERM.....AK
LONG TERM......TDH
AVIATION.......SKOWRONSKI
HYDROLOGY......TDH







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